The belt-driven tape cartridges of the Von Behren patent, U.S. Pat. No. 3,692,255, incorporated herein by reference, are commonly referred to as "data cartridges." A data cartridge typically includes a housing defining a thin, generally rectangular enclosure. The housing contains a length of magnetic recording tape which is wound upon a pair of tape reel hubs. The magnetic recording tape is driven by an elastomeric drive belt which, in turn, is driven by a single, reversible drive motor. The drive belt provides rapid acceleration and deceleration of the recording tape in either direction. The drive belt is stretched along a drive belt path generally defined by a drive roller, a pair of corner rollers, and part of the tape pack wound on each hub.
The tape, driven by the drive belt, is under a certain amount of tension during operation of the data cartridge. The tape tension must not fall below a certain level as the tape passes from hub to hub or else contact between a read/write head and the tape may be insufficient to allow successful data transfer. Conversely, the maximum drive force, i.e., the force which must be applied to rotate the cartridge drive roller, must not exceed the power rating of the motor in the associated drive. In short, data cartridges must meet minimum tape tension specifications while simultaneously operating within maximum allowable drive force specifications to achieve acceptable performance of a data cartridge in a drive. Meeting both specifications may be difficult, especially since drive force is at least partially dependent on tape tension, meaning that an increase in tape tension has the effect of increasing drive force.
To further optimize data cartridge performance, it is extremely desirable to maintain uniform minimum tape tension and operate within specified drive force parameters during recording and playback. Changes in temperature, for example, may cause tape tension and drive force characteristics to vary considerably. This variability may lead to undesirable consequences such as stalling of the drive at low operating temperatures or insufficient tape tension at high operating temperatures. Therefore, reducing the temperature dependence of tape tension and drive force characteristics will improve data cartridge performance.